1. Field of the Invention
The present invention relates generally to computer systems architecture, and, more particularly, to a method and apparatus for the display of progressive and interlaced video content on a display.
2. Background of the Related Art
It is believed that digital video disc (DVD) is the next generation of optical disc storage technology that is expected to eventually replace the audio compact disc (CD), videotape, laser disc, and CD-ROM (read only memory). Currently, DVD is available in two formats, DVD-Video, which can store video such as movies, for example, and, DVD-ROM, which can store computer programs for use with a computer.
The display of motion video on computer system displays has become increasingly popular. However, one difficulty encountered with DVD-Video on a computer system is the format conversion that the computer system needs to perform to display the DVD-Video. This mainly results because the display scanning technique used for computer monitors is different from that for standard television screens.
Referring to FIGS. 1A and 1B of the drawings, two conventional scanning techniques for displaying images on different types of displays are shown. FIG. 1A illustrates an interlaced scanning technique (also referred to as interleaved scanning), which is performed on conventional television sets in accordance with the National Television Standard Committee (NTSC) format. A conventional television screen has 525 scan lines, which make up a frame. Images appear on the television screen by scanning the odd lines of the frame first, and, subsequently, scanning the even lines of the frame. The odd and even lines of the screen each make up their own respective field. Accordingly, a frame includes two fields (i.e., an xe2x80x9coddxe2x80x9d field that includes the odd lines of the frame and an xe2x80x9cevenxe2x80x9d field that includes the even lines of the frame). In accordance with the NTSC format, 60 fields are displayed per second on a television screen, which results in a frame rate of 30 frames per second.
As opposed to interlaced scanning, some displays use a progressive scanning technique as shown in FIG. 1B. Progressive scanning requires twice the frequency as interlaced scanning to achieve the same refresh rate. Such progressive scan displays are typically more expensive than interlaced displays, and are used in most cases as a computer monitor for a computer system. In progressive scanning, the 525 lines of the display are scanned in sequential order, which enables a more superior picture quality than that of the interlaced displays.
DVD often contains both progressive and interlaced formats on a single disc. DVD/MPEG2 (Motion Picture Expert Group, standard 2) decoding outputs standard NTSC signals. The 60 fields/second interlaced television content is presented as it is in the original NTSC format. However, for 24 frames/sec. progressive film content, 60 fields/sec. interlaced NTSC signal is generated using 3:2 pulldown algorithm, such as the one defined by the MPEG specification. Each decoded frame is presented as two interlaced fields. For example, frame A is presented as A1 and A2. Some fields are duplicated according to the repeat field control signal in the MPEG2 stream. When showing DVD/MPEG2 video on a progressive computer monitor, the video display needs to be adjusted for field or frame contents, in order to decrease motion artifacts.
FIG. 2 illustrates a conventional 3:2 pulldown technique for converting a 24 frames/sec. progressive film content 205 to a 60 fields/sec. interlaced format in accordance with the NTSC format. Frames 210 of the progressive video content are converted to fields 220 of the NTSC standard. The first frame A is converted to three fields, in which the third field is the repeat of the first field. That is, frame A is decoded to A1, A2 and A1 again. The second frame has only two fields B2 and B1. The 3:2 pattern is then repeated, as shown, for the subsequent frames. For field-based content, one method can be used to present each field separately with one line offset for field 2. For frame-based content, another method is needed to remove the repeated fields to present one frame at a time. Currently field skip is achieved through software interrupt service. However, due to interrupt latency problems, the software-based method can be slow and/or unreliable.
The present invention is directed to providing a hardware system for adjusting the video capture and video overlay for the field-based and frame-based contents.
A technique for processing video data in which a decoder receives video data and decodes into fields based on content format of the video data. The decoder generates a flag associated with the content format. A memory stores the decoded fields and a controller coupled to the decoder and the memory receives the decoded fields and the flag. The controller also stores the fields in the memory and retrieves the fields from the memory in a selected format based on the flag.